Contact lenses with the object of continuous wear for a long term are made of silicone rubber prepared from polydimethyl siloxanes. High water content contact lenses are made of poly-N-vinylpyrrolidone polymers. Since the silicone rubber contact lenses are very water-repellent and greatly different from the cornea in thermal properties such as thermal conductivity and thermal diffusivity, they give a foreign body sensation, particularly a burning sensation despite having oxygen permeability. Contact lenses made from silicone rubber are uncomfortable to wear. Further, the silicone rubber is soft and elastic, making it difficult to conduct precise mechanical treatments such as cutting, grinding, and polishing. Many attempts for making the surface of silicone rubber lenses hydrophilic have been undertaken, but no completely satisfactory contact lens has been developed. Since the high water content contact lenses contain about 60% to about 80% by weight of water, they have the disadvantages that they are weaker in quality of material than low water content contact lenses, are easily contaminated with inorganic and organic compounds in tears which penetrate and accumulate into the lenses during the use, and are bad in maintenance of lens contour due to the evaporation of water during the use and, therefore, the refractive power thereof easily changes.
Conventional hydrogel materials made from 2-hydroxyethylmethacrylate (HEMA) have poor oxygen permeability and poor oxygen transport to the eye through the absorbed water molecules. Water has low oxygen permeability. Contact lenses made from 2-hydroxyethylmethacrylate monomers are slowly dehydrated and the amount of oxygen transported to the cornea is reduced upon exposure to atmospheric air for longer periods. Eye irritation, redness and other corneal complications can result and hence restrict use of the lenses to limited periods of wear.
Silicone-hydrogel films are used to make extended wear soft contact lenses due to their high oxygen permeability, flexibility, comfort and reduced corneal complications. Silicone-hydrogels have overcome some of the obstacles for long periods of wear beyond conventional hydrogels because these silicone-hydrogels make comfortable soft contact lenses with higher oxygen permeability than the conventional hydrogel materials. However, these silicone-hydrogels have deficiencies. For example, many of the silicone-hydrogels used linear blocks of dimethylpolysiloxanes to improve oxygen permeability. It is known that polysiloxanes, which contain α,ω-terminal unsaturated groups bonded through divalent hydrocarbon groups or amino-containing hydrocarbon groups (heterocarbon groups), have been used in preparing soft, contact lenses. Lower molecular weight unsaturated siloxane-polyether copolymers with the α, ω-divinylpolysiloxanes have also been used in combination with unsaturated polysiloxane-polyether copolymers and a compatibilizing additive. These polymers contain linear hydrophobic dimethylpolysiloxane chains, which form hydrophobic regions within the polymer and may cause corneal complications or difficulties in conducting precise mechanical treatments.
Methacryloxypropyltris-(trimethylsiloxy)silane monomers have been used to prepare silicone-containing hydrogels. The (meth)acryloxypropyltris -(trimethylsiloxy)silane is hydrophobic and is used in preparing polyurethane-silicone polymers. These polyurethane-silicone polymers contain blocks of hydrophobic silicone. Contact lenses made from these polymers may cause eye discomfort because of the hydrophobic regions within the polymer.
Silicone-hydrogels are typically made from acrylate or methacrylate functionalized silicone monomer that are polymerized with hydrophilic monomers, such as hydroxyethyl methacrylate (HEMA), N-vinylpyrrolidone (NVP) and other monomers such as methyl methacrylic acid (MA), and dimethylacrylamide (DMA), in the presence of crosslinker and free radical or photoinitiators. Crosslinking agents generally have two or more reactive functional groups at different sites of the molecule. Typically, these sites contain polymerizable ethylenic unsaturation groups. During polymerization to form the silicone-hydrogel, they form a covalent bond with two different polymer chains and form a stable three-dimensional network to improve the strength of the polymer. Crosslinking agents conventionally used in contact lenses include ethylene glycol dimethacrylate and trimethyloylpropane trimethacrylate. Other useful crosslinking agents include diethyleneglycol dimethacrylate, bisphenol A dimethacrylate, diglycidyl bisphenol A dimethacrylate and dimethacrylate-terminated polyethylene glycol and reactive linear polyether modified silicones. The oxygen permeability of these silicone-hydrogels is affected by the chemical structure of the acrylate or methacrylate functionalized silicone monomer and choice of the other monomers containing reactive carbon-carbon double bonds that are used in preparing the crosslinked polymer.
Silicone-hydrogel contact lens materials are typically made using either hydrophobic mono-functional silicone monomers or multi-functional hydrophilic silicone monomers followed by secondary surface treatment. Mono-functional silicone monomers are often used in the contact lens industry over multi-functional silicone monomers since the latter lead to increased rigidity in the lenses made therefrom. The known mono-functional silicone monomers, however, may have deficiencies. For example, monofunctional siloxane-polyether (meth)acrylates are susceptible to air oxidation. Monofunctional (meth)acryloxy functional siloxanes that contain 1,4-substition the (meth)acryloxy group to the siloxane group on a six-member ring, such as for example, (meth)acrylic acid 2-hydroxy-4-[2-bis-(trimethylsiloxy)methylsilanyl-ethyl]-cyclohexyl ester, form highly ordered copolymers which may inhibit the permeability of oxygen through the silicone-hydrogel.
Although the state of the art for soft contact lenses has been improving, silicone-based materials still possess major shortfalls, like sub-optimal surface wettability and oxygen permeability, and the need for compatibilizers in preparing the polymer. In an effort to overcome these drawbacks, current state of the art technology uses either expensive secondary surface treatments called “plasma oxidation”, or internal wetting agents. These approaches may decrease oxygen permeability or require the use of compatibilizers, which adds costs during the manufacturing process.
Hence, there remains a need for hydrophilic silicone monomers with inherently advantageous wettability, stability to air oxidation, high oxygen permeability and high solubility in the other reactive monomers used to make the polymer without the need for compatibilizers. The trisiloxane containing a 3-(meth)acryloxy-substituted (hydroxylcyclohexyl)ethyl group of the present invention can be used to make contact lenses without the drawbacks of poor wettability, oxidative instability, less than optimal oxygen permeability, expensive surface treatments and processing costs associated with using compatibilizer necessary with the silicone containing materials of the present art.